Current methods of measuring angle of arrival vary from simple staring lens systems with a blur circle centroid measuring detector configuration (such as a 4-quadrant detector element), to very complex arrays, or alternatively utilize scanning mechanisms or rotating/nutating reticles. Techniques utilizing scanning of any mechanization are of no value in the detection of a single descrete event in time, such as a laser pulse. Infrared System Engineering, John Wiley & Sons, 1969; and of particular applicability, section 6.4 of that chapter.
Those non-scanning methods which require lenses are limited to relatively narrow spectral regions by the transmission of the lens material, and cannot be used to sense high power lasers due to the possibility of detector damage from concentration of power by the lens.
Some non-imaging methods have been investigated that solve these two problems, but are very complex both optically and electronically. In addition such methods require complex trigonometric calculatons to convert the 3 dimensional angles measured to true azimuth and elevation.
It is highly desirable that the two (vertical and horizontal) channels of the locator be independent, i.e., laser movement in space in one axis does not alter the output of the channel measuring perpendicular to that axis. It is further highly desirable that these vertical and horizontal measurements be in the true azimuth (outer gimbal) and elevation (inner gimbal) axes, since this angular coordinate system is used by virtually all systems with which the locator may be required to interface. A major feature of this invention is the very simple achievement of such independent azimuth and elevation measurement capability without crosstalk from motion in the perpendicular axis.